I am late.

I rush in a panic past the bullet-marked walls and shell-damaged buildings of central Mostar. Composer Nigel Osborne waits for me on the rubbly pavement, beneath Bosnia’s unforgiving midday sun.

Sweating my apologies, I explain that I’m meant to interview him about his latest commission for a chamber music festival at an elegant house in the Borders of Scotland – Music at Paxton. I am almost embarrassed to mention such gentle pursuits here. We’re in Bosnia to work, through music, with children suffering from war trauma. I pass stray cats and old men missing limbs, who shelter in the shade of roofless buildings. Scotland seems impossibly unreal. And very far away.

Not so for Osborne. For him this is all part of one boundless creative life. His latest work – The Painters In My Garden – is inspired by the celebrated Glasgow Boys. Much of their work was done in Cockburnspath, now home to Osborne. The roof of his cottage even features in one of their pictures, he points out with some pride. “The fact that this wonderful work was done in and around where I live was personally very interesting to me.”

The new piece is for three flutes, an instrumentation that Osborne describes as “perfect, because I have the possibility of one colour and of many colours. I was very interested in this palette. To me, that was the paint box I needed to do these things.” Appropriately the music references five paintings: The Herd Boy and A Day Dream by E A Walton, Fast Castle by John Thomson of Duddingston, Playmates by George Henry and Hard At It by James Guthrie, pictured.

Well known as a composer, Osborne is perhaps even more famous for his strong social conscience. In the 1990s, horrified by the Balkan genocide he saw on his television, he downed tools as Reid Professor of Music at Edinburgh University and smuggled himself into besieged Sarajevo to do what he could. Working as a de facto civil servant for the Bosnian government, delivering bread and providing music for children as they sheltered from the shelling in basements kept him there for years.

And although it might seem unrelated, that political conscience also guides his work as a composer. Even more than the local geographical connection with the Glasgow Boys of Painters, he cites their “gritty social realism” as “important to me – I feel very close to them”.

If Osborne’s political gospel is social inclusivity, leading his instincts as a creative artist, then his international “musical interventions” are his evangelism. On a stony bank beside the river Neretva, in the shadow of the reconstructed old bridge of Mostar, we gather our troupe of children from the Special Needs Centre for our first performance of the week. It is a musical written by children in Serbia, but based on a Roma gypsy tale. Their story tells of a young boy – an outcast from society because of his appearance – who is recognised by a wise king for his intelligence and bravery, and brought back into the social fold.

It isn’t hard to see why Osborne has chosen this material for the children. Among the performers are not just Roma children from a camp nearby, but also an ethnically mixed group of young music theatre workers from the town of Srebrenica. He has brought them to his summer camp, he says, because “I think what they are doing is beautiful, and I want to encourage them”.

Given his first-hand experiences of nationalism gone horribly wrong in the Balkans and elsewhere, I wonder if Osborne felt at all tentative in writing something so rooted in Scottish national culture as Painters. As well as the paintings themselves –national treasures – he has also worked in traditional Scottish folk melodies. Even Sir Walter Scott gets a look in at one point.

Does his knowledge of the dark side of nationalism make him wary of the subject? “Yes, it does,” he replies firmly. “My work against nationalism and fascism has made me very conscious of that. But I see in the majority of Scottish nationalism something inclusive and benign.”

And we’re back to his guiding principle –inclusivity. For Osborne, the broader the creative life, the better: “We need every flower in the garden,” as he puts it. There is nothing contrary about work for a Scottish music festival and work with children in the war-torn corners of the world. “I’m a modernist. I don’t believe that we can be exclusive and limited now.”

Is he, I wonder, implying that the “classical” music world (often critical of his biggest compositions) is too narrow and stuck-up? He answers moderately. “There is a place for sharp focus – there always is in art. But I don’t think it is the best way of taking care of the world at the moment. At the moment, I’m more concerned with taking care of the whole garden of music.”

And just when you thought he might be busy enough, taking care of that garden now means for Osborne a passionate interest in neuroscience. Co-director of the Institute for Music in Human and Social Development in Edinburgh, he is leading the field in the development of music and neuroscience in its therapeutic application.

Of his forthcoming premiere at Paxton on July 19, he says that The Painters In My Garden is “the beginning of something, not the end”. With confidence he states that there will be “Glasgow Boys orchestral works” from him in the future. “Oh yes”, he says, to my questioning look, “I’m not going to stop there. We’re going on.”

A statement which quite clearly could stand for his life as a whole.

The Painters In My Garden, performed by the Scottish Flute Trio, will premiere on July 19 at Paxton House near Berwick Upon Tweed as part of Music at Paxton. For further information on the chamber music festival, which runs from today until July 24, see www.musicatpaxton.co.uk